The present invention relates to an automatic lubricator for lubricating a machine automatically, and relates more particularly to such an automatic lubricator which effectively prevents the leaking of lubricating oil.
FIG. 1 shows a prior art automatic lubricator (10) for lubricating a machine automatically. This automatic lubricator (10) comprises an oil container (11) having an air vent (111) at the top side and an inside annular flange (112) downwardly raised from the top side, a piston (12) reciprocated in the oil container (11) and peripherally sealed with a rubber seal ring (121), a coil spring (13) mounted in the oil container (11) between the inside annular flange (112) and the piston (12) to give a downward pressure to the piston (12), a container holder (14) covered on the bottom open side of the oil container (11) and having a vertical oil outlet (141) at the bottom side and a horizontal oil inlet (142) on the periphery, a valve assembly (15) which comprises a valve body (151) fastened to the oil inlet (142), having an oil feeding passage (153), a first inside flange (154) and a second inside flange (155) around two opposite ends of the oil feeding passage (153), and an expanded head (152) for the connection of an oil feeder, a spring (157) mounted in the oil feeding passage (153) and stopped at the first inside flange (154), and a ball (156) mounted in the oil feeding passage (153) and forced by the spring (157) into engagement with the second inside annular flange (155) to close the oil feeding passage (153). When lubricating oil is fed into the oil container (11) through the valve assembly (15), the piston (12) is moved upwards. After the feeding of lubricating oil, the piston (12) is forced by the coil spring (13) to squeeze lubricating oil out of the vertical oil outlet (141) for lubricating the mechanical parts of the machine for example the bearings. The coil spring (13) is made from a steel wire by winding, and then heat treated. As illustrated in FIGS. 2 and 3, the uniformity of the diameter D and the contained angle Q between each two turns affect the compression performance of the coil spring (13). If the coil spring (13) is not accurately positioned and the both ends of the coil spring (13) are not closely attached to the inside wall of the oil container (11) and the top side of the piston (12), the coil spring (13) may curve outwards when compressed (see the dotted line of FIG. 3).If the coil spring (13) curves outwards when compressed, the piston (12) will be forced to tilt. If the piston (12) is tilted, it cannot be smoothly moved in the oil container (11) to force lubricating oil out of the oil container (11) through the vertical oil outlet (141). As illustrated in FIG. 4, the piston (12) has a plain bottom side. When lubricating oil is fed into the oil inlet (142), the unstable feeding pressure of lubricating oil tends to cause the piston (12) to tilt. Furthermore, because the air vent (111) is made on the top side of the oil container (11), dust may pass through the air vent (111) to the inside of the oil container (11) to contaminate the piston (12) and the rubber seal ring (121). If the rubber seal ring (121) is covered with dust, the piston (12) may be jammed in the oil container (11) and unable to be reciprocated. Please see also FIG. 5. When the lubricating oil feeder is attached to the expanded head (152) of the valve body (151) of the valve assembly (15), the ball (156) is forced backwards from the second inside flange (155), permitting lubricating oil to pass through the oil feeding passage (153) to the inside of the oil container (11). When the feeding of lubricating oil is stopped, the ball (156) is forced forwards by the spring (153) to stop against the second inside flange (155) and to prevent a leakage of lubricating oil. However, because the valve body (151) and the ball (156) are respectively made from metal, the second inside flange (155) and the ball (156) will wear with use quickly, causing the ball (156) to be unable to engage with the second inside flange (155) firmly. If the ball (156) and the second inside flange (155) are not firmly engaged with each other, lubricating oil will leak out of the valve body (151).